Semiconductor component and production method

ABSTRACT

Semiconductor component and method for production of a semiconductor component. The invention relates to a semiconductor component having a semiconductor chip, which is arranged on a substrate, in one embodiment on a chip carrier, and an encapsulation material, which at least partially surrounds the semiconductor chip. The chip carrier is at least partly provided with a layer of polymer foam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application is a divisional application of U.S.application Ser. No. 11/817,520, filed Sep. 24, 2007, and claimspriority to German Application No. DE 10 2005 010 272.7, filed Mar. 3,2005, and is also based on PCT/DE2006/000308, filed Feb. 20, 2006, allof which are herein incorporated by reference.

BACKGROUND

The present invention relates to a semiconductor component and to amethod for production of a semiconductor component.

A semiconductor chip that is mounted on a chip carrier or a leadframeand is electrically connected or bonded thereto by using connectingwires, for example, is usually encapsulated in a molding compound inorder to form a semiconductor housing. These semiconductor housings arenormally produced from a plastic. Thermosetting plastics, in particularepoxy resin, are used particularly extensively for this purpose.

However, these encapsulating compounds have inadequate adhesion to theboundary interfaces or surfaces of the semiconductor chip or of the chipcarrier which they enclose or adjoin. This leads to increased failureand fault risks for the semiconductor component, and not least to devicequalifications not being passed.

In order to ensure sufficient adhesion in accordance with therequirements made of the semiconductor component and in accordance withthe device qualifications, in the prior art a highly targeted andcomplicated selection and evaluation of suitable molding compounds wasundertaken and the chip carrier, leadframe or substrate surfaces weretreated by using complicated mechanical methods, such as roughening thesurfaces to be connected, etc. Moreover, physico-chemical methods suchas plasma-etching, electrolytic coating with adhesion-enhancing layersbased on inorganic, metallic compounds were carried out in order toensure sufficient adhesion.

However, the abovementioned mechanical or physico-chemical methods forachieving an enhancement of adhesion between the molding compound and asubstrate give rise to very high process costs and the disadvantage ofrestricting the application to electrically conductive surfaces.Moreover, these methods also led only in part to the desired or requiredenhancement of the molding compound adhesion.

For these and other reasons, there is a need for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates two perspective sectional views through a layercomposed of a block copolymer.

FIG. 2 illustrates a molecular representation of a polymer foam.

FIG. 3 illustrates a semiconductor component which has been at leastpartly coated with an organic substance.

FIG. 4 schematically illustrates the formation of the layer of polymerfoam in two method processes.

FIG. 5 illustrates a schematic sectional view through a semiconductorcomponent with encapsulation.

FIG. 6 illustrates two schematic sectional views through the layer ofpolymer foam during the transfer molding process.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which isillustrated by way of illustration specific embodiments in which theinvention may be practiced. In this regard, directional terminology,such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc.,is used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments of the present inventioncan be positioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims.

The present invention provides a method for production of asemiconductor component, and a corresponding semiconductor component,wherein sufficient adhesion between the molding compound from which thehousing of the semiconductor component is produced and a substrate ormetallic leadframe on which a semiconductor chip is arranged is achievedin a simple and therefore also cost-effective manner.

One embodiment provides a method for production of a semiconductorcomponent, wherein the method includes:

-   -   applying a solution of an organic substance to a substrate, in        one embodiment to a chip carrier, wherein the organic substance        has polymers and functional molecules which are suitable for        reacting and crosslinking to form a layer of polymer foam;    -   producing the polymer foam by applying heat to the organic        substance, wherein the temperature is kept below 200° C.;    -   crosslinking the polymer foam by applying heat to the polymer        foam, wherein the temperature is kept above 200° C.;    -   encapsulating a semiconductor chip arranged on the substrate        with a plastic material.

Coating polymers have intrinsically surface-active groups or can becombined with a series of highly active groups such silanes orisocyanates which ensure strong adhesion on the polymeric metallic orceramic support. The disadvantage of such highly reactive polymergroups, however, is that, on account of their high reactivity they arethen normally no longer available for a chemical reaction with themolding compound from which the housing surrounding the semiconductorchip is formed, whereby the binding of the encapsulating material has tobe ensured in some other way. Therefore, before or after the die/wirebonding, the substrate or the chip carrier or the leadframe is coatedwith the solution of the organic substance, which has polymers andfunctional organic molecules which react and crosslink after applicationto form a polymer layer. The solution can be applied to the substrate byusing a dipping, spraying, dripping or stencil printing method. Duringcuring, the polymer coating leads to a splitting off of CO, CO₂ or othermolecular segments that split off at relatively high temperatures fromthe polymer chain, whereby a solid polymer foam layer arises. It is alsopossible to use special block copolymers in which the foam arises as aresult of the thermal decomposition of a thermolabile Co component,e.g., polypropylene oxide. The polymer foam layer has pores into whichthe still molten oligomer chains can diffuse during encapsulation withthe epoxy resin molding compound, which entails not only the increasedchemico-physical adhesion between the polymers (polymer foam and moldingcompound, e.g., epoxy resin) on account of the larger surface area andthe pores of a foam but also a fixed mechanical anchoring of the moldingcompound. Furthermore, the polymer foam has the advantage that a verylow dielectric loss occurs at high switching frequencies on account ofthe low dielectric constant (ε<3) and the low loss factor tan δ (<10⁻²)of the material, particularly if the foam is also used as “low-Kdielectric” on the chip top side.

In accordance with a further embodiment, a process of producing anelectrical connection between the chip carrier and the semiconductorchip arranged on the chip carrier is carried out prior to applying thesolution to the chip carrier.

As an alternative to this, a process of producing the electricalconnection between the chip carrier and the semiconductor chip arrangedon the chip carrier can be carried out after applying the solution tothe chip carrier.

The process of producing the electrical connection is carried out byusing a die/wire bonding process.

By way of example, the organic substance used can be a polyimide or ahigh-performance thermoplastic.

As an alternative to this, the organic substance used can be a blockcopolymer in which the foam arises as a result of the thermaldecomposition of a thermolabile Co component. This has the advantagethat the pores of the foam can be produced particularly finely.

The thermolabile Co component is polypropylene oxide.

In a further exemplary embodiment of the invention, the layer of polymerfoam is produced with pores of an order of magnitude which predominantlylies in the sub-μm range.

In one embodiment, a thermosetting plastic, in particular epoxy resin ora silicone resin, is used as plastic material for encapsulating thesemiconductor chip.

In a further exemplary embodiment of the invention, the encapsulating iscarried out with an epoxy resin molding compound by using a transfermolding process.

Furthermore, the invention provides a semiconductor component having asemiconductor chip, which is arranged on a substrate, in particular on achip carrier, and a housing, which at least partially surrounds thesemiconductor chip, wherein the chip carrier is at least partly providedwith a layer of polymer foam. By using the layer of polymer foamprovided on the chip carrier, leadframe or substrate, particularly goodadhesion in the manner described above to the encapsulating compoundcomposed of plastic material, in particular composed of a thermosettingplastic, is obtained in simple and cost-effective manner, whereby faultrisks of the semiconductor component are minimized and the quality ofthe semiconductor component is thus improved, also with regard tospecific device qualifications.

In one embodiment, the layer of polymer foam is provided on the chipcarrier at the boundary surfaces with respect to the housing, with theresult that it is possible to ensure sufficient adhesion of the housingto the chip carrier.

In accordance with one embodiment of the invention, the substrate or thechip carrier is produced from metal.

As an alternative to this, the substrate or the chip carrier can beproduced from ceramic or polymer or a plastic substrate. The enhancementof the molding compound adhesion by applying a layer of polymer foam canbe obtained at all surfaces i.e. at surfaces of any materials.

In one embodiment, the layer of polymer foam has a dielectric constantof ε<3, in particular <1.5. Very low energy losses are thus obtained athigh switching frequencies on account of the low dielectric constant andthe low loss factor tan δ (<10⁻²) of the material.

In accordance with one embodiment of the invention, the layer of polymerfoam is produced from polyimide or a high-performance thermoplastic.

In one embodiment, the layer of polymer foam is produced from a blockcopolymer in which the foam arises as a result of the thermaldecomposition of a thermolabile Co component.

Furthermore in one embodiment, the thermolabile CO component ispolypropylene oxide.

In one embodiment, it is furthermore advantageous if the layer ofpolymer foam has pores of an order of magnitude which predominantly liesin the sub-um range. The still molten oligomer chains diffuse into thepores during the encapsulation with the epoxy resin molding compound,which entails not only the increased chemico-physical adhesion betweenthe two polymers (polymer foam and molding compound) on account of thelarger surface area and the pores of a foam but also a fixed mechanicalanchoring of the molding compound.

In accordance with a further embodiment of the invention, the housing isproduced from a plastic material.

In this case, the plastic material is a thermosetting plastic, inparticular epoxy resin.

In one embodiment, it is furthermore advantageous if the housing isproduced by using a transfer molding process.

The layer of polymer foam has a thickness within a range of between 2nm-10 μm depending on the polymeric system, the concentration of thestarting solution and the processing conditions such as coatingtechnique, temperature, solvent type, coating rate, etc. FIG. 1perspectively illustrates two sectional views through a layer 1 composedof a block copolymer. FIG. 1 a) illustrates an illustration of the layer1, such as can be applied to a substrate 2 (not illustrated), before athermal treatment for forming a foam has been carried out. The layer 1still has separate phases here, the black filled circles representing athermolabile Co component which decomposes under the action oftemperature and thus forms the pores 3 in the layer 1, as illustrated inFIG. 1 b), the open circles illustrated in the layer 1 here representingvacancies or air in the material.

FIG. 2 illustrates a molecular representation of a polymer foam such ashas been described with regard to FIG. 1 and such as can be used for theproduction of the semiconductor component 4 (not illustrated) accordingto the invention. Here, (t.Bu-O-CO)₂O has been incorporated as thermallylabile group into the main polymer chain, which decomposes below T_(g)of the polymer and thus leads to the formation of the pores in the nmsize range.

FIG. 3 illustrates a semiconductor component 4, which has been at leastpartly coated with an organic substance from which the layer 1 ofpolymer foam is formed in two further method processes. In this example,the layer 1 has been applied on the surface of the semiconductor chip 5and the upper and lower surface of the substrate 2 or chip carrier.Here, too, the semiconductor chip 5 has already been electricallyconnected to the substrate 2 by using conducting wires 6.

FIG. 4 schematically illustrates the formation of the layer 1 of polymerfoam in the two method processes that follow the method processillustrated in FIG. 3. As viewed from top to bottom, this figureillustrates the layer 1 composed of an organic substance, which haspolymers and functional organic molecules which react and crosslinkafter application to form a polymer layer, as a continuous black bar,which reflects the state of the coating illustrated in FIG. 3. Under theaction of heat, wherein the temperature is kept below 200° C., duringthe curing of the layer 1, a splitting off for example of CO, CO₂ andother molecular segments or thermolabile groups that split off atrelatively high temperatures occurs. These drive out from the materialand leave behind pores 3 in the form of voids in the predominantlysub-μm size range. In a further method process, which is carried outunder the action of temperatures above 200° C., the polymer foam thusformed then crosslinks to form a solid composition or layer 1 havingextremely fine pores 3 or voids.

FIG. 5 illustrates a schematic sectional view through a semiconductorcomponent 4 with an encapsulation or a housing 7 surrounding thesemiconductor chip 5 arranged on a substrate 2 or chip carrier. Theinterfaces of the substrate 2 and of the semiconductor chip 5 withrespect to the housing 7 are coated with a layer 1 of polymer foam,thereby ensuring a very good adhesion of the molding compound of thehousing 7 composed of epoxy resin thereon.

Finally, FIG. 6 illustrates two schematic sectional views through thelayer 1 of polymer foam during the transfer molding process for formingthe housing 7 composed of epoxy resin. In FIG. 6 a) which illustratesthe beginning of the transfer molding process, the molding compoundhaving epoxide chains 8 is applied to the surface of the layer 1 ofpolymer foam which has the pores 3. During the progress of the transfermolding process, i.e. here also during the process of encapsulating thesemiconductor component 4 (not illustrated) with the epoxy resin moldingcompound, the oligomer chains or epoxide chains 8 can diffuse into thepores 3 in the layer 1 of polymer foam, as illustrated in FIG. 6 b).This obtains, as already mentioned, not only the increased physicaladhesion between the polymer foam and the molding compound on account ofthe larger surface area and the pores of a foam, but also a fixedmechanical anchoring of the molding compound.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments illustrated and describedwithout departing from the scope of the present invention. Thisapplication is intended to cover any adaptations or variations of thespecific embodiments discussed herein. Therefore, it is intended thatthis invention be limited only by the claims and the equivalentsthereof.

What is claimed is:
 1. A semiconductor component comprising: a substrateat least partly provided with a layer of polymer foam; a semiconductorchip arranged on the substrate; and a housing which at least partiallysurrounds the semiconductor chip and covers at least portions of thesubstrate, wherein the layer of polymer foam is disposed on thesubstrate at boundary surfaces between the substrate and the housing,and wherein material of the housing is disposed within pores in thepolymer form to anchor the housing thereto.
 2. The semiconductorcomponent of claim 1, comprising wherein the chip carrier is producedfrom metal.
 3. The semiconductor component of claim 1, comprisingwherein the chip carrier is produced from ceramic or polymer.
 4. Thesemiconductor component of claim 1, comprising wherein the layer ofpolymer foam has a dielectric constant of ε<1.5.
 5. The semiconductorcomponent of claim 1, comprising wherein the layer of polymer foam isproduced from polyimide or a high-performance thermoplastic.
 6. Thesemiconductor component of claim 1, comprising wherein the layer ofpolymer foam is produced from a block copolymer in which the foam arisesas a result of the thermal decomposition of a thermolabile Co component.7. The semiconductor component of claim 6, comprising wherein thethermolabile Co component is polypropylene oxide.
 8. The semiconductorcomponent of claim 1, comprising wherein the layer of polymer foam haspores of an order of magnitude which predominantly lies in the sub-μmrange.
 9. The semiconductor component of claim 1, comprising wherein thehousing is produced from a plastic material.
 10. The semiconductorcomponent of claim 8, comprising wherein the plastic material is athermosetting plastic.
 11. The semiconductor component of claim 1,comprising where the housing is produced by a transfer molding process.12. The semiconductor component of claim 1, comprising where the layerof polymer foam has a thickness within a range of between 2 nm - 10 μm.13. A semiconductor comprising: a semiconductor chip having a firstmajor surface and an opposing second major surface; a carrier, the firstmajor surface of the semiconductor chip mounted on the carrier; apolymer foam layer disposed on the second major surface of thesemiconductor chip and on at least portions of the carrier not coveredby the semiconductor chip; and an encapsulation material encapsulatingthe semiconductor chip and covering at least portions of the carrier,wherein the encapsulation material is disposed within pores in thepolymer foam layer to anchor the encapsulation material thereto.
 14. Thesemiconductor of claim 13, comprising: wherein the polymer foam is acrosslinked polymer foam.
 15. The semiconductor of claim 13, wherein thelayer of polymer foam includes pores of an order of magnitude whichpredominantly lies in the sub-μm range.
 16. The semiconductor of claim13, wherein a thermosetting plastic encapsulates the semiconductor chip.17. The semiconductor of claim 16, wherein the encapsulating material isan epoxy resin molding compound.
 18. The semiconductor of claim 16,wherein the semiconductor chip is electrically connected to the carrierwith one or more wires, and wherein connection points of the wires tothe carrier are covered by the polymer foam layer.